Thermoplastic polymers are commonly used to manufacture various shaped articles that may be utilized in applications such as automotive parts, food containers, signs, and packaging materials. Shaped articles may be prepared from polyester by a number of melt extrusion processes known in the art, such as injection molding, compression molding, blow molding, and profile extrusion.
The most common polyester currently used is polyethylene terephthalate (PET). Due to recent trends toward sustainability and reduced use of petroleum, alternatives to PET are being investigated. Poly(trimethylene terephthalate), herein abbreviated 3GT, also referred to as PTT or polypropylene terephthalate, may be useful in many materials and products in which polyesters such as PET are currently used, for example molded articles. 3GT has properties including a semi-crystalline molecular structure.
British Patent 578097 disclosed the synthesis of 3GT in 1941. 3GT may be prepared using 1,3-propanediol derived from petroleum sources or from biological processes using renewable resources (“bio-based” synthesis). The ability to prepare 3GT from renewable resources makes it an attractive alternative to PET. 3GT produced from renewable sources of 1,3-propanediol is commercially available from E.I. du Pont de Nemours and Company (DuPont) under the tradename SORONA. DuPont pioneered a way to produce the 1,3-propanediol from renewable resources including corn sugar.
The melt viscosity or intrinsic viscosity (IV) of 3GT varies depending on how it is prepared and is roughly correlated to the molecular weight. Previous applications often used 3GT polymerized to lower IV. This approach may lead to low impact performance (impact resistance), and has critical moisture requirements because of the low molecular weight of the polymer. The low IV resins are predominantly used in glass-reinforced materials, which to some degree mitigate the effect of low IV on impact performance.
Use of reinforcements may lead to higher viscosity, poor surface gloss, and poor scratch and mar resistance and other esthetic effects. The increased interest in 3GT as a replacement for PET is prompting the use of 3GT in applications that do not permit the use of reinforcing materials. These applications using unreinforced 3GT may have problems with inadequate impact resistance and/or moisture concerns when 3GT with lower IV is used.
Another polyester of interest is poly(tetramethylene terephthalate), herein abbreviated 4GT, also referred to as PBT or polybutylene terephthalate.
Compositions comprising poly(trimethylene terephthalate) and a thermoplastic polyester have been disclosed (e.g., JP2614200, JP2004-300376 and JP2006-290952).
Monofunctional organic acids are known to interchange with polyester, leading to lower molecular weight polymers. Similarly, salts of organic acids are known to cause molecular weight loss.
Using higher viscosity polyester may improve impact resistance, but the high viscosity may lead to processing difficulties. Higher viscosity polymers may decompose at higher temperatures and may have thermal limits that preclude viscosity reduction by operating at very high temperatures.
Toughening (increased impact resistance) may also be useful for articles prepared from the compositions. Toughening polyester has been achieved using an ionomer modifier, an epoxide-containing copolymer such as ethylene/n-butyl acrylate/glycidyl methacrylate (EBAGMA) (e.g., WO85/03718, WO2007/089644, and U.S. Pat. No. 5,091,478). See also, JP2614200, JP2004-300376, and JP2006-290952.
Methods to lower viscosity and thereby improve injection molding of 3GT compositions, while simultaneously maintaining as much “bio-based” content as possible, are desirable. Increasing toughness and/or impact resistance is also desirable.